During oilfield drilling and borehole completion operations tubular strings may be handled in the form of a drill string, a casing string or a liner string for drilling and/or lining the borehole, etc. To grip a tubular and the tubular string, a tubular gripping tool may be used. In some operations, such as casing drilling and/or casing running, tubular gripping tool in the form of a casing clamp may be used to grip the string at its upper end.
A tubular gripping tool may be connected for manipulation by a top drive or other device, the entire assembly being suspended in a rig or derrick by a draw works, if desired.
Tubular gripping tools may include gripping means that engage the tubular being handled. Gripping means may include, for example, devices that mechanically or frictionally engage the tubular including, for example, slips, jaws, packers, expandable members, etc., catch devices that hook under a shoulder on the tubular being handled, such as elevators, etc. and/or other members that exert a mechanical or physical force or field on the tubular to engage it. Tubular gripping tools may also include spears, which are intended to extend into the bore of a tubular being handled. An external gripping tool may include a center spear and gripping means that engage an outer surface of a tubular to be handled. In use, the spear is inserted into the inner diameter of the tubular and the gripping means grip the outer surface thereof. An inside gripping clamp may include a spear with gripping means thereon, such that when the spear extends into the bore of a tubular being handled, the gripping means are positioned for engagement of an inner wall of the bore of the tubular.
An example of an inside gripping clamp is described in U.S. Pat. No. 6,742,584 of Appleton, and assigned to the present assignee TESCO Corporation. An example of an external gripping clamp is described in U.S. Pat. No. 6,311,792 of Scott, which is also assigned to the present assignee.
A spear of a tubular gripping clamp may carry various tubular handling mechanisms. For example, a spear may include a seal thereabout which is selected to engage and create a seal against the inner diameter of the tubular being handled. During operation, drilling fluid, commonly called mud and which can be liquid or gas-based, is pumped down through the spear and the seal creates a seal against the inner diameter to maintain fluid pressure in the tubular string. The seal generally is passive and operates against a pressure differential.
In a well control incident, it may be desirable to shut in the well, including sealing the upper end of the tubular string. If such an incident occurs during the use of a gripping clamp, well control may be achieved by reliance on the seal about the clamp's spear. As a next step, or where a failure of the passive seal is encountered, it may be desirable to support the tubular string in the floor of the derrick/rig and to remove the casing clamp from the tubular, such that the tubular string can be capped. In a situation where both the draw works and the spear seal fail, the well may be very difficult to control. In such a situation, a blow out preventer may be useful for carriage on the spear.
In addition or alternatively, a spear may carry other tubular handling mechanisms including for example, launching systems, such as for plug launching or tool release apparatus.
For spear-carried tubular handling mechanisms, such as a well control system or a launching system, an actuation system may be required to control the operation of the system. Because the tubular handling mechanism is carried on the spear, it may be necessary that at least a portion of the actuation mechanism be carried on the spear. Because the spear is often a rotating part, actuation mechanisms for spear-carried tubular handling mechanisms can add to the complexity of tubular handling systems.